1. Field of the Invention
The present invention relates to a sheet surface reversing device for reversing a front surface and a back surface of a sheet by feeding the sheet reversely on the way of conveyance of the sheet along a conveying direction, and an image forming apparatus having such a sheet surface reversing device, such as a copying machine, a facsimile, a printer or combination thereof.
2. Related Background Art
Conventionally, for example, in a sheet surface reversing device incorporated into a copying machine, a rotary member generally called a flapper has been rotated by a solenoid to switch a sheet conveying direction. And, a technique in which an elastic member is provided on a distal end of the flapper is also well-known.
Incidentally, the sheet may include a normal paper (plain paper), a resin sheet having a small thickness (as a substitute article for the normal paper), a post card, a paper board, an envelope, a plastic thin film or the like.
FIG. 8 shows an example of a sheet surface reversing device, in which an elastic member made of Mylar (trade name), for example, is used for a guide piece (conveying path switching member) 101 of a rotary member 100. In FIG. 8, a sheet enters from a direction B1, and the sheet can be switched toward a direction C1 by rotating forwardly and reversely surface reverse rollers 104 and by abutting the guide piece 101 serving as a valve against a wall of the convey path. However, in the example of FIG. 8, as shown in FIG. 9, during the reversing operation for the sheet, in dependence upon a condition of the sheet (curl, rigidity and/or material), a leading end of the sheet may be caught by a distal end of the guide piece 101, with the result that the leading end of the sheet may be folded or the sheet may be jammed at worst.
Another conventional example is disclosed in Japanese Utility Model Publication No. 6-38838, for example. FIG. 10 shows a characteristic portion of such another example, in which a distal end of an elastic guide piece 101 is protruded outwardly through a hole 105 formed in a guide plate 103. With this arrangement, during the reverse feed of the sheet, the leading end of the sheet can be prevented from being caught by the distal end of the guide piece 101.
Further, a further conventional example is disclosed in Japanese Patent Application Laid-Open No. 59-118482. FIG. 11 shows a characteristic portion of such an example. After a sheet passed between guide portions 112 and 113 is conveyed in a direction indicated by the arrow a, the sheet is conveyed by a surface reverse roller (not shown) in a direction indicated by the arrow b. Above the guide portion 112, there are disposed a guide portion 110 and an elastic guide piece 111 attached to the guide portion 110. The guide piece 111 has a pectination (comb) shape and comprises protruded portions 111a and recessed portions 111b, and distal ends of the protruded portions 111a block or close a conveying path defined between the guide portions 112 and 113 and are located at a sunken position lower than a plane of the guide portion 113 extending along the arrow b. With this arrangement, when the sheet is conveyed in the direction indicated by the arrow a, the sheet can easily advance while pushing out the protruded portions 111a; whereas, when the sheet is conveyed in the direction indicated by the arrow b, the sheet is offered to be prevented from entering into the conveying path between the guide portions 112 and 113 and the leading end of the sheet is offered to be prevented from being caught.
However, the above-mentioned conventional examples have the following disadvantages.
First of all, in the example shown in FIG. 10, if the elastic guide piece 101 has a uniform shape (for example, rectangular shape) over the entire length in the longitudinal direction, the corresponding hole 105 also extends continuously along the length of the guide piece 101. As a result, depending upon the curled state of the sheet, the leading end of the sheet being conveyed may be caught by the hole 105 or the sheet may escape out of the guide portion. In order to avoid this, an arrangement as shown in FIG. 12 can be considered.
A guide piece 101 has a pectination (comb) shape and comprises protruded portions 101b and recessed portions 101a, and a guide plate 103 opposed to the protruded portions 101b is provided with holes 105 which is associated with the protruded portions 101b and into which free ends of the corresponding protruded portions 101b are inserted. By providing such holes 105 divided along the longitudinal direction, even when a sheet S is advanced from a direction indicated by the arrow B1, the sheet S can be prevented from escaping outside through the holes. Further, in order to switch the conveying path, side edges of a sheet S which is apt to be caught (for example, in FIG. 12, side edges of a sheet having A4 size or B5 size) are passed positions off the holes 105 (over the recessed portions 101a).
However, even with the arrangement as shown in FIG. 12, due to skew-feed of the sheet for any reason or in dependence upon the curled state of the sheet, the sheet may be caught by the recessed portion 101a or the hole 105, and, thus, adequate reliability is not ensured.
Further, in the example shown in FIG. 11, since the recessed portions 111b of the guide piece 111 are spaced apart from a stepped portion of the guide 113 more or less, the same problem that the leading end of the curled sheet is apt to be caught arises. Further, since the pectination shape is used, the rigidity is reduced to easily cause deformation, with the result that the protruded portions 111a may be floating from the stepped portion to catch the sheet.
An object of the present invention is to provide a sheet surface reversing device in which a sheet is prevented from being jammed due to interference between a leading end of the sheet conveyed reversely and a distal end of a conveying path changing member, and stable sheet conveyance can be achieved, and an image forming apparatus having such a sheet surface reversing device.
To achieve the above object, according to the present invention, there is provided a sheet surface reversing device comprising a sheet conveying path through which a sheet is conveyed, reverse feeding means for reversely feeding the sheet conveyed through the sheet conveying path, a sheet surface reverse conveying path for directing the sheet reversely fed from the reverse feeding means, and a conveying path changing member rotatably disposed at a branched portion between the sheet conveying path and the sheet surface reverse conveying path, wherein, in a state that a distal end of the conveying path changing member abuts against an inner wall of the sheet conveying path, the distal end guides the sheet to be reversely fed into the sheet surface reverse conveying path, and wherein interference avoiding means for avoiding interference between the sheet reversely fed and the distal end of the conveying path changing member are provided on the inner wall of the sheet conveying path.
With this arrangement, when the sheet is reversely fed by the reverse feeding means, the rotating distal end of the conveying path changing member abuts against the inner wall of the sheet. conveying path, and the interference avoiding means conceals the rotating distal end not to be seen from the reverse feeding means. Thus, the interference avoiding means can cause a leading end of the sheet reversely fed (trailing end of the sheet conveyed through the sheet conveying path) to pass over the rotating distal end of the conveying path changing member thereby to avoid the interference between the leading end of the sheet and the rotating distal end of the conveying path changing member, thereby guiding the sheet reversely fed into the sheet surface reverse conveying path smoothly. In this way, the sheet can be prevented from being jammed due to the changing of the conveying path changing member.
In the present invention, preferably, the conveying path changing member may include a rotary member provided at the branched portion, and an elastic guide member provided on the rotary member and capable of abutting against the inner wall.
With this arrangement, since the guide member abutting against the inner wall of the sheet conveying path is an elastic member, a rotating distal end of the guide member is closely contacted with the inner wall of the sheet conveying path not to protrude from the interference avoiding means, thereby enhancing the sheet jam preventing effect.
Further, in the present invention, preferably, a longitudinal configuration of the guide member may be made substantially uniform so that the guide member abuts against the inner wall throughout the longitudinal length of the guide member.
With this arrangement, since the guide member has the substantially uniform configuration, the sheet cannot be caught by the guide member and the guide member itself is deformless, and, thus, stable performance can be achieved.